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power supply sometimes works

O

orange

Jan 1, 1970
0
I've got problem with one PSU. Its occasionaly working.
Sometimes when I turn the switch ON nothing happens and then when I
turn it OFF, for a sec it starts and (normally) shutsdown immediately.


what could be the problem?

It is very old Amiga 2000 switching PSU, similar to PC (+12V,
+5V..etc).

please help
 
M

mike

Jan 1, 1970
0
orange said:
I've got problem with one PSU. Its occasionaly working.
Sometimes when I turn the switch ON nothing happens and then when I
turn it OFF, for a sec it starts and (normally) shutsdown immediately.


what could be the problem?

It is very old Amiga 2000 switching PSU, similar to PC (+12V,
+5V..etc).

please help

The supply may require some minimum load on one or all outputs
to function.
mike

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O

orange

Jan 1, 1970
0
it behaves the same, load or no load, sometimes it works but its pure
luck
 
Check your heat sink & the heat tranfer cream, it could due to poor
heat tranfer to the
heat sink, i have this problum also.
 
R

Ron(UK)

Jan 1, 1970
0
orange said:
it behaves the same, load or no load, sometimes it works but its pure
luck
It`s probably going to be a failing electrolytic in the mains side of
the chopper circuit - I dont have a diagram but I`d expect it to be in
the region of between 1 and 10 uf. Be aware that there are dangerous
voltages around there, maybe even when it`s unplugged.

Ron
 
K

kip

Jan 1, 1970
0
Pull then all and change them if you dont have an ESR Meter.

kip
 
R

Ron(UK)

Jan 1, 1970
0
orange said:
It would be my guess that it`s one of the little orangey ones with the
black stripe under the silver heatsink, The type visible in pic 0011,
right on the edge of the board. Also look for one similar near the
chopper transistor - That`ll be the one on the black heatsink I reckon.

You`d really need to check all the electrolytics with an esr meter to be
sure. First off I'd get all that crap out of there if I were you, and
remember that there might be a charge stored in those 200 volt smoothers.

Ron
 
B

budgie

Jan 1, 1970
0
I've got problem with one PSU. Its occasionaly working.
Sometimes when I turn the switch ON nothing happens and then when I
turn it OFF, for a sec it starts and (normally) shutsdown immediately.


what could be the problem?

It is very old Amiga 2000 switching PSU, similar to PC (+12V,
+5V..etc).

please help

Serious question: Have you tried replacing the switch?
 
O

orange

Jan 1, 1970
0
ok thanks all, I was going to clean it thoroughly but since
electrolytics can leak I thought experienced users might see signs of
leakage if not cleaned,
I was also hoping it might be the switch, but after checking with
ohmmeter it works ok.

err, what exactly is esr meter?
My voltmeter can check capacitance (but I need to desloder them and put
in special place for checking probably because of cable capacitance,
right?) and it can see if capacitors are shorted.

I can check resistance between various points, if that could be of any
help for solving the problem?
 
K

kip

Jan 1, 1970
0
Why don't you just replace the filter caps and end your misery.

kip
 
O

orange

Jan 1, 1970
0
OK, kip, but which ones ARE filter caps? Please have a look at photos
and tell me..
 
J

James Sweet

Jan 1, 1970
0
orange said:
ok thanks all, I was going to clean it thoroughly but since
electrolytics can leak I thought experienced users might see signs of
leakage if not cleaned,
I was also hoping it might be the switch, but after checking with
ohmmeter it works ok.


They can leak, but usually they fail without any visible signs. That wave of
caps made with bad electrolyte did tend to bulge and leak though.
 
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